Coil turn insulation in vicinity of tap lug



Dec. 12, 1961 F. J. CORNELL COIL TURN INSULATION IN VICINITY OF TAP LUG Filed June 30, 1958 INVENTOR. FRANK J. CORNELL BY i z E Z FIG. 2

ATTORNEY United States Patent Office 3,013,106 Patented Dec. 12, 1961 3,013,106 con. TURN INSULATION IN vIorNITY or TAP LUG This invention pertains to the art of electrical transformers and more particularly to means for electrically insulating the tap lugs on a transformer coil.

The invention is particularly applicable to the art of high frequency transformers and will be described with particular reference thereto, although it will be appreciated the invention has broader applications.

In the art of high frequency transformers, it is conventional to form either the primary or secondary, or both, of a single layer helix of copper tubing having a rectangular cross section. Tap lugs are brazed to the Outer surface of the turns of the helix where it is desired to tap the helix. The individual turns of the helix are then insulated one from the other by means of an insulating tape wrapped spirally and progressively around the conductor which comprises the coil.

In the past, dilficulty has been experienced insulating the coil in the location of the tap lugs. Thus even with considerable overlapping of the tape turns, there was an appreciable area adjacent each tap Where it was difficult to provide insulation between the turns. It has therefore been conventional to leave the areas exposed and provide sheets of insulating material wedged between the turns in the region of the bare areas. Notwithstanding this, oftentimes difliculty was experienced with the sheets of insulation shifting relative to the turns and exposing these bare areas to possible short circuiting with adjacent turns of the helix.

A further difficulty with this arrangement for electrically insulating the tap lug, was the extra buildup of tape insulation which result from the 'efiorts of the coil winder to minimize the extent of the exposed areas adjacent to the tap lugs.

The present invention contemplates a new and improved arrangement whereby the above problems are overcome and the insulation of the tap lugs is relatively simple.

In accordance with the present invention, the means for insulating the tap lug are in the form of an insulating member comprised of a pair of first portions laying against the sides of the conductor forming the coil and having a longitudinal length greater than the longitudinal length of the tap lug and integrally joined by a pair of spaced second portions, each laying against the outer side of the conductor forming the coil helix one on each side of the pig. The first portions preferably have a width equal to the width of the conductor. In a slightly more limited aspect of the invention, each of the first portions includes a third portion of a width or length equal to one half the thickness of the lug which extends outwardly over the lug immediately adjacent to the point of connection of the lug to the outer surface of the conductor.

Further in accordance with the invention, the insulating means comprises a flat sheet of electrically insulating material adapted to be formed generally into the shape of a U-shaped channel with the legs of the channel engaging the sides of the conductor and the base of the channel being comprised of two spaced portions adapted to engage the outer surface of the conductor and w'th portions of the leg intermediate the spaced portIons extending outwardly over the sides of the tap lug.

The principal object of the invention is the provision of a new and improved means for electrically insulating the tap lug on a helical coil which is simple in construction, economical to manufacture and easily installed.

Another object of the invention is the provision of a new and improved means for insulating a tap lug on a helical coil which eliminates the problems of insulation buildup at the intersection of the tap lug and the outer surface of the coil and which is prevented from shifting from its position by means of the electrical insulation.

The invention may take physical form in certain parts and arrangements of parts, the preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawing which is a part hereof and wherein.

FIGURE 1 is a perspective view of a fragment of a coil turn at the location of a tap lug with a preferred embodiment of the insulating means of the present invention in position and showing in phantom lines, the electrical insulating tape which is wound thereover.

FIGURE 2 is a top elevational view of a sheet of the insulating material after cutting and before bending to the shape shown in FIGURE 1.

Referring now to the drawings wherein the showings are for the purposes of illustrating a preferred embodiment of the invention only, and not for the purposes of limiting same, the figures show a fragmentary length of an elongated electrical conductor A having a generally rectangular cross-sectional shape defined by a pair of longitudinally extending sides 10 having a predetermined width w and at least a longitudinally extending edge 11 having a predetermined width 1. Normally, the sides 10 are parallel to each other and are flat, although it will be appreciated that this is not necessarily so. In a like manner, the edge 11 is normally fiat, although it will be appreciated that it could also have other shapes, such as an arcuate shape.

A coil tap lug B has one end fixed by brazing or the like to the edge 11 and as will be seen, the tap lug has upper and lower surfaces 15 generally flush with the surfaces 10 of the conductor A which surfaces 15 are spaced a distance equal to t. It will be appreciated, however, that the spacing of the surfaces 15 may differ slightly from that of the spacing of the surfaces 10.

In the embodiment of the invention shown, a tap lug B has a predetermined longitudinal length L and may have any desired transverse length.

For the purpose of electrically insulating the conductor A in the vicinity of the tap lug B, insulating means are provided comprised of a pair of spaced first portions 20 of a width generally equal to the width w of the conductor A and a length L at least greater than the longitudinal length l of the tap lug B which portions 20 lie against the sides 10 of the conductor A. The portions 20 are integral with each other by means of spaced second portions 21 of a dimension generally equal to the dimension 1 which portions lie against the edge 11, one on each side of the tap lug B. These second portions 21 have edges 22 spaced a distance equal to the dimension I so that the edges 22 will abut against the longitudinal sides 16 of the tap lug B.

The insulating means also includes a third portion 25 between the edges 22 which laps over a fringe of the upper and lower surfaces 15 of the tap lug B immediately adjacent to the surfaces 10 of the conductor A. Preferably the portions 25 have an outer edge of a dimension just equal to the dimension 1 and an inner dimension where it adjoins the first portion 20 just slightly greater than the dimension L.

The insulating means C in accordance with the preferred embodiment of the invention, is formed from a flat sheet of insulating material indicated generally by the reference character D of FIGURE 2 having a length between edges 30 equal generally to the sum of the width w of the sides 10 and the thickness of the edge 11 and has a width between side 31 at least greater than the dimension L. The sheet D has a slit 3-3 parallel to and midway between the ends 30 of a length equal to the dimension 1, which slit 33 at its ends, is terminated in a pair of transversely extending slits 34 extending in equal directions on each side of the slit 33 of a length generally equal to the dimension t. It will be noted that the slits 34 are slightly convex in shape towards the slit 33.

After the slits indicated are formed, the insulating member is then bent generally into the form of a U-shaped channel to form the portions 20, 21 and with the slits 33, 34 opening up to provide an opening so that the insulating means C may he slipped over the tap lug B into the position in FIGURE 1. Thereafter theinsulating tape may be spirally wound around the conductor A and because of the insulation provided by the insulating means C, it is not necessary in any way to bunch the insulating tape in the corner formed by the tap lug B and the conductor A. e

The present insulation has solved a very serious problem in the manufacture of transformers of the type described and has proven very'efiective in practice. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification, and it is my intention to include all such modifications and alterations insofar as they come within the scope of the appended claims. 7

Having thus described my invention, I claim:

1. In the combination of a one-piece insulator positioned on an elongated conductor at a tap lug thereon,

the conductor having spaced longitudinally extending sides of predetermined width and a longitudinally extending edge between said sides, the tap lug being attached to the conductor at said edge and extending transversely outward therefrom, and the tap lug having opposite sides which extend substantially flush with said sides of the conductor and which have a predetermined extent parallel to the length of the conductor, the improvement which comprises said insulator comprising a bendable flat sheet of electrical insulation material formed into a generally U-shaped channel and mounted on the conductor at the tap lug,

said'sheet having a pair of opposite first portions each having an extent away from the other at least substantailly at great as said predetermined width of said longitudinally extending sides of the conductor and engaging said sides of the conductor completely thereacross, each of said first portions having a length parallel to the length of the conductor which is greater than said predetermined extent of the tap lug parallel to the length of the conductor, said sheet having an opening therein between said first portions which has a length substantially equal to said predetermined extent of the tap lug parallel to the length of the conductor and snugly receiving said tap lug, said sheet at the opposite ends of said opening presenting second portions, each of which is disposed between said opposite first portions and each of which is integral with both said opposite first portions and interconnects the latter, said second portions having an extent between said first portions substantially equal to the exent of said edge of the conductor between said sides thereof and engaging said edge at the opposite ends of the tap lug, all of said portions being so dimensioned that before said sheet is formed into a U-shape, none of said portions overlap:

2. The insulator of claim 1 wherein said opening before said sheet is formed into the shape of a U is in the form of an elongated slit extending across the insulator, and wherein there are provided a pair of additional slits at the opposite ends of said first-mentioned slit which extend transverse to said first-mentioned slit, said additional slits 1 having a length substantially equal to the extent of said edge of the conductor between said sides thereof.

3. The insulator of claim 2 wherein said additional slits intersect said first-mentioned slit intermediate their ends and are convex toward each other.

' 4. In the combination of a one-piece insulator positioned on an elongated conductor at a tap lug thereon, the

conductor having spaced longitudinally extending sides of predetermined width and a longitudinally extending edge between said sides, the tap lug being' attached to the conductor at said edge and extending transversely outward therefrom, and the tap lug having opposite sides which extend substantially flush with said sides of the conductor and which have a predetermined extentrparallel to the length of the conductor, the improvement which comprises said insulator being formed from a'flat sheet of electrical insulating material into a generally U-shape in cross-section having a pair of opposite, substantially parallel first portions, each having an extent at least substan tially as great as said predetermined width of said longitudinally extending sides of the conductor and engaging said sides completely thereacross, each of said opposite first portions of the insulator having a length parallel to the length of the conductor which is greater than said predetermined extent of the, tap lugs parallel to the length -of the conductor, said insulator having a pair of spaced second portions, each of which interconnects said first portions and is integral with said first portions and extends transverse thereto, said second portions having an extent between said first portions substantially equal to the extent of said edge of the conductor between said sides thereof and engaging said edge at the opposite ends of the taping, and said insulator having an opening therein between said first portions and between said spaced second portions, said opening having a length substantially equal to said predetermined extent of the tap lug parallel to the length of the conductor and snugly receiving saidtap' lug, and said opening in the insulator having a'width substantially equal to the extent of said edge of the conductor between said sides thereof, all of said portions being so dimensioned that before said sheet is formed into a U-shape, none of said portionsoverlap. I

5. The insulator of claim 4 wherein there is provided an integral portion at each edge of the opening in overlapping engagement with the tap lug thereat.

7 References Cited in the file of this patent UNITED STATES PATENTS 644,690

' FOREIGN PATENTS 385,699 GreatBritain Ian. 5, 1933 OTHER REFERENCES Publication I Get Sound Bus Iointsthe Easy Way, published 'in Electrical World, Dec. 29, 1952 (page 91 relied on).

Shellenberger ct al Mar. 6, 1900 

